The display portion of a portable electronic device such as a portable notebook computer usually has an addressable viewing screen area where information is displayed, by the effect of changes in light, in individual pixel increments of liquid crystal material, that passes through the viewing screen from behind. While it is the addressable matrix in the viewing screen that supplies the information in the display, the ability to see the information is directly dependent on the light that is passed through the viewing screen.
Some of the optical considerations in handling the light distribution and achieving uniform illumination have been discussed in the art in an article by Whitehead et al. titled "Light-Distribution Methods for Backlighting LCD's" in the 1992 SID DIGEST pages 419-422; and in an article by J. M. Gordon et al. titled "Achieving Uniform Illumination with Multiple Asymmetric Compound Parabolic Luminaires" in the SPIE Vol. 2016 Nonimaging Optics (1993) pages 27-37.
As the art progresses into portable electronic apparatus, a new major consideration is taking on increasing importance. It is becoming necessary to get the most performance out of the apparatus for the weight and volume involved. In portable apparatus the power is usually provided by a battery that occupies a portion of the package volume. There is limited ability to increase battery size without also affecting the weight and volume of the overall apparatus package. It is thus essential to provide the apparatus with an energy consumption efficiency that will expand the time the unit can operate on a battery.
One of the most energy hungry and wasteful energy drains in the display portion of an electronic apparatus is in the light that is employed in the back lighting of the display. It is of great importance to maximize the efficiency ratio relating the light that is projected at the viewer with the light that is produced in the light bulb. There is however a constraint, that is more serious in portable apparatus, that the aspect ratio of any optical path for backlighting will be such that while the light must come from behind the viewing screen over a broad area, any space perpendicular to the screen occupied by the light path may have to be quite small.
The art, in addressing this constraint, has developed the use of a transparent wedge shaped light pipe member of a material such as a clear polymer, that is positioned supporting the screen area with the tapered dimension of the wedge aligned with one edge of the screen area. A long light bulb serving as a light source is positioned within a reflector and is used to direct light along it's length, into the wide portion of the wedge shaped light pipe. The light is dispersed in the wedge shaped light pipe and the direction is changed so that it passes through the display screen evenly over the display area.
In such a configuration, however, there are losses in connection with the many parts of the light path from the light bulb to the viewer of the display screen.